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Aviation History
1963
1963 - 0712.PDF
FLIGHT International, 9 May 1963 of the undercarriage bay immediately behind the roots of the main-gear beams. On the starboard side near the rear of Section 43, aft of what will normally be the first-class accommodation, is a galley door 33in by 65in. Beneath the floor of this section is a pressurized and heated (but not ventilated) freight hold, with a capacity of 390 cu. ft. The hold extends a distance of 199in (from Station 481 to 680) and has a depth of 44in. About half-way along to starboard is an inward (upward) hinging plug-type door 48in wide and 35in high, with a mean sill level of 60in from the ground. Forward of this hold is the main electrics/electronics bay, and to the rear is the main air-conditioning bay. Body section 46 contains four overwing emergency-escape hatches, each of the 20in by 38in pattern used on the 707. Immed iately aft of the rear spar a 63in-deep keel member runs down the centreline between the main-wheel compartments, terminating at Station 962. From Station 870 to 900 this keel beam incorporates cut-outs for an optional APU. Behind this station is the aft cargo compartment, which has a volume of 465 cu ft and extends back 215in to Station 1177. Maximum depth of this hold is 54in, and the 48in by 35in door has a sill 61 in (mean) above the ground. The front edge of this door is 98in from the front of the compartment, and even this location was rendered possible only by arranging for the starboard wing fillet fairing to slide aft on rails. Station 1183, the end of this section, is also the location of the pressure bulkhead. Built as part of Section 46, it is a flat vertical plate stiffened by a grid of stabilizing members, and with a central aperture 32in by 76in closed by the plug-type rear door. Section 48, aft of the pressure bulkhead, is a more complex structure than the pressurized tube ahead, since it incorporates large cut-outs and bears the loads from the engines and tail. Primary structure consists of two beams, one forming each side of the section, consisting of the stringer-stiffened skin, plate frames each some 24in deep, and longitudinal torque boxes above and below. Between these beams is a space occupied by the No 2 engine inlet duct and the passenger stairway. The stairs consist of an upper fixed portion and a lower section hinged about its upper (forward) end and retracted upwards by a hydraulic jack which breaks the support struts. Stair operation can be controlled from the head of the stairway or from the ground, and in the absence of hydraulic power manual pumping may be used for raising and gravity for lowering. The stair struts are stressed to bear both tensile and compressive loads. On each side of the brightly lit stairway are access doors to air- conditioning, hydraulic and fire-extinguishing equipment, and the stairway roof is flat trim blanking off the No 2 inlet duct. The retractable tailskid is located beneath the fixed portion of stairway. On either side are hung Nos 1 and 3 engines. Their front mountings, which bear loads in all directions, are machined steel forgings with upper and lower arms cone-bolted to the engine and a root diffused away into the frame at the Section 46 pressure bulkhead. The rear mount picks up the engine at a single point, and carries only vertical and lateral loads. The centre engine is hung at the extreme end of the body, with no structure around it except for a close-fitting hinged cowling and isolated by vertical and horizontal firewalls. It is hung from mounts basically similar to those used for the side engines. These in turn are attached to the underside of a horizontal support rib, integral with the horizontal firewall, supported by a stiffened-skin/rib structure riveted to the rear fin spar. Primary structure of the fin comprises a front and rear spar, stiffened skin panels and plate ribs. The vertical tail is swept at the extraordinary angle of 55° to bring the horizontal tail as far aft as possible and thus increase its moment arm and enable its size to be reduced. The front fin spar is anchored to the pressure bulkhead, the fin rear spar to the bulkhead at Station 1342 (forward of No 2 engine front firewall), and the stiffened fin skins are extended down into body section 48 as the inboard faces of the upper torque boxes. Ahead of the front spar is a frame/skin fairing extending forward to the centre-engine intake, and an upper removable leading edge containing a hot-air duct. To the upper rear tip of the fin is hinged the tailplane, which is a single two-spar structure designed for rigidity and pivoted at approximately its aerodynamic centre of pressure. All tail surfaces are subject to some sonic vibration from the side engines, and features intended to confer a long life in this environment include the use of stress-relieved materials, symmetrical sections, laminated webs and panels, metal and glass-fibre honeycomb, and the elimina tion of punched or blanked holes (all perforations are drilled or 685 routed). The rudder and elevator are described in the section dealing with flying controls. Each of the three units of the landing gear has a single shock strut and twin wheels equipped with brakes. All units are retracted hydraulically, by "A" system, and can be lowered by gravity and locked down by hand cranks. Each main leg is of modified 4330 steel heat-treated to 220,000/240,0001b/sq in and protected by a new Cd/Ti plating process. Similar material is used for the nose gear, and design goals for the complete undercarriage include 60,000 landings for primary components, 8.000 for replaceable parts such as pins and bushes, 600 normal stops between brake replacements and wheel roll life of 10,000 miles. Systems It is appropriate at this stage to record the close co-operation between Boeing and their main accessory suppliers. When Boeing had chosen such firms as Loud, Menasco and AiResearch, engineers from these firms went on to the payroll at Renton for periods of many months and then returned to their own companies when the equipment was ready for production. Flying controls Control of the 727 about all three axes is accom plished by surfaces geometrically similar to those of the 707 and 720 but fully powered throughout. All surfaces are driven by actuators in both A and B hydraulic systems; in addition, in the event of loss of both systems the ailerons and elevator automatically revert to manual operation and a third stand-by system provides power for the lower rudder. Manual reversion increases pilot input forces, but places no restriction on aircraft speed. Lateral control is effected by inboard ailerons, outboard ailerons and flight spoilers. With flaps extended, all these surfaces are used, but when the flaps are retracted the outboard ailerons are locked out of circuit. There are seven metal-honeycomb spoilers on the upper surface of each wing. Three are located ahead of the inboard flap. The inner two of this group are used only on the ground to destroy lift after touchdown and increase wheel-brake traction; these surfaces, which are alternatively known as the ground speedbrakes, are mechanically sequenced by main-undercarriage oleo compression. The remaining spoiler of the inboard group, and the four spoilers ahead of the outboard flap, are all linked to the aileron control circuit. The latter rotates a powered rate-cam (known as the mixer box) on each side of the aircraft coupled to duplicated cables linking the individual hydraulic packages at each spoiler station. The outermost pair of spoiler sections are driven by hydraulic system A, as are the ground spoilers; the remaining three sections of flight spoiler are in system B. For use as airbrakes, all ten flight spoilers may be opened in unison to the maximum deflection of 45° to permit a letdown rate of up to 6,000 ft/min. When all the spoilers are open they continue to assist lateral control, because rotation of the pilots' aileron wheels partially closes the spoilers on the upgoing wing. Inboard and outboard ailerons are of conventional construc tion, apart from the trailing-edge tabs which are filled with metal honeycomb. Movement of the pilots' wheels is transmitted by cables, cams and rods to a single hydraulic power unit in the port main-gear well. The pack incorporates actuators in both A and B hydraulic systems, and also allows direct manual control in the absence of all hydraulic power. It provides three rotary outputs. One locks out the manual tab system, another drives the valve input and the third shaft drives the aileron bus cables leading out to the ailerons (and connected by a pogo-spring push rod to the flight-spoiler system). One cable system is coupled to the control tab on the trailing edge of both inboard (high-speed) ailerons. The other cable-run is connected to a mechanical linkage driving the inboard aileron main surfaces and to a further mechanical linkage driving the outboard (low-speed) ailerons. The linkage to the latter incorporates a mechanical input from the flap system which dis connects the outboard ailerons except when the flaps are lowered. The tabs on the outboard ailerons are balance tabs linked to the fixed wing structure. In the absence of hydraulic power, roll demands by the pilot drive the control tabs on the inboard ailerons directly, and, if the flaps are lowered, the main surfaces of the low-speed outboard ailerons. The autopilot is the Sperry SP-50, and its servo motor is coupled to the aileron output from the pilots' handwheels. Pilot feel is provided by a spring cartridge in the input to the aileron
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